// Conditional to use more aggressive fail-fast behaviors when debugging.
#define DEV_DEBUG

// This file contains general utilities to aid in development.
// It is distinct from unit test Assert classes.
// Classes here generally shouldn't be exposed publicly since
// they're not particular to any library functionality.
// Because the classes here are internal, it's likely this file
// might be included in multiple assemblies.
namespace Standard
{
	using System;
	using System.Diagnostics;
	using System.Threading;

	/// <summary>A static class for verifying assumptions.</summary>
	internal static class Assert
	{
		// Blend and VS don't like Debugger.Break being called on their design surfaces.  Badness will happen.
		//private static readonly bool _isNotAtRuntime = (bool)System.ComponentModel.DesignerProperties.IsInDesignModeProperty.GetMetadata(typeof(System.Windows.DependencyObject)).DefaultValue;

		private static void _Break()
		{
			//if (!_isNotAtRuntime)
			{
#if DEV_DEBUG
				Debugger.Break();
#else
                Debug.Assert(false);
#endif
			}
		}

		/// <summary>A function signature for Assert.Evaluate.</summary>
		public delegate void EvaluateFunction();

		/// <summary>A function signature for Assert.Implies.</summary>
		/// <returns>Returns the truth of a predicate.</returns>
		public delegate bool ImplicationFunction();

		/// <summary>
		/// Executes the specified argument.
		/// </summary>
		/// <param name="argument">The function to execute.</param>
		[Conditional("DEBUG")]
		public static void Evaluate(EvaluateFunction argument)
		{
			IsNotNull(argument);
			argument();
		}

		/// <summary>Obsolete: Use Standard.Assert.AreEqual instead of Assert.Equals</summary>
		/// <typeparam name="T">The generic type to compare for equality.</typeparam>
		/// <param name="expected">The first generic type data to compare.  This is is the expected value.</param>
		/// <param name="actual">The second generic type data to compare.  This is the actual value.</param>
		[
			Obsolete("Use Assert.AreEqual instead of Assert.Equals", false),
			Conditional("DEBUG")
		]
		public static void Equals<T>(T expected, T actual)
		{
			AreEqual(expected, actual);
		}

		/// <summary>
		/// Verifies that two generic type data are equal.  The assertion fails if they are not.
		/// </summary>
		/// <typeparam name="T">The generic type to compare for equality.</typeparam>
		/// <param name="expected">The first generic type data to compare.  This is is the expected value.</param>
		/// <param name="actual">The second generic type data to compare.  This is the actual value.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void AreEqual<T>(T expected, T actual)
		{
			if (null == expected)
			{
				// Two nulls are considered equal, regardless of type semantics.
				if (null != actual && !actual.Equals(expected))
				{
					_Break();
				}
			}
			else if (!expected.Equals(actual))
			{
				_Break();
			}
		}

		[Conditional("DEBUG")]
		public static void LazyAreEqual<T>(Func<T> expectedResult, Func<T> actualResult)
		{
			Assert.IsNotNull(expectedResult);
			Assert.IsNotNull(actualResult);

			T actual = actualResult();
			T expected = expectedResult();

			if (null == expected)
			{
				// Two nulls are considered equal, regardless of type semantics.
				if (null != actual && !actual.Equals(expected))
				{
					_Break();
				}
			}
			else if (!expected.Equals(actual))
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that two generic type data are not equal.  The assertion fails if they are.
		/// </summary>
		/// <typeparam name="T">The generic type to compare for inequality.</typeparam>
		/// <param name="notExpected">The first generic type data to compare.  This is is the value that's not expected.</param>
		/// <param name="actual">The second generic type data to compare.  This is the actual value.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void AreNotEqual<T>(T notExpected, T actual)
		{
			if (null == notExpected)
			{
				// Two nulls are considered equal, regardless of type semantics.
				if (null == actual || actual.Equals(notExpected))
				{
					_Break();
				}
			}
			else if (notExpected.Equals(actual))
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that if the specified condition is true, then so is the result.
		/// The assertion fails if the condition is true but the result is false.
		/// </summary>
		/// <param name="condition">if set to <c>true</c> [condition].</param>
		/// <param name="result">
		/// A second Boolean statement.  If the first was true then so must this be.
		/// If the first statement was false then the value of this is ignored.
		/// </param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void Implies(bool condition, bool result)
		{
			if (condition && !result)
			{
				_Break();
			}
		}

		/// <summary>
		/// Lazy evaluation overload.  Verifies that if a condition is true, then so is a secondary value.
		/// </summary>
		/// <param name="condition">The conditional value.</param>
		/// <param name="result">A function to be evaluated for truth if the condition argument is true.</param>
		/// <remarks>
		/// This overload only evaluates the result if the first condition is true.
		/// </remarks>
		[Conditional("DEBUG")]
		public static void Implies(bool condition, ImplicationFunction result)
		{
			if (condition && !result())
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that a string has content.  I.e. it is not null and it is not empty.
		/// </summary>
		/// <param name="value">The string to verify.</param>
		[Conditional("DEBUG")]
		public static void IsNeitherNullNorEmpty(string value)
		{
			IsFalse(string.IsNullOrEmpty(value));
		}

		/// <summary>
		/// Verifies that a string has content.  I.e. it is not null and it is not purely whitespace.
		/// </summary>
		/// <param name="value">The string to verify.</param>
		[Conditional("DEBUG")]
		public static void IsNeitherNullNorWhitespace(string value)
		{
			if (string.IsNullOrEmpty(value))
			{
				_Break();
			}

			if (value.Trim().Length == 0)
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies the specified value is not null.  The assertion fails if it is.
		/// </summary>
		/// <typeparam name="T">The generic reference type.</typeparam>
		/// <param name="value">The value to check for nullness.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void IsNotNull<T>(T value) where T : class
		{
			if (null == value)
			{
				_Break();
			}
		}

		[Conditional("DEBUG")]
		public static void IsDefault<T>(T value) where T : struct
		{
			if (!value.Equals(default(T)))
			{
				Assert.Fail();
			}
		}

		[Conditional("DEBUG")]
		public static void IsNotDefault<T>(T value) where T : struct
		{
			if (value.Equals(default(T)))
			{
				Assert.Fail();
			}
		}

		/// <summary>
		/// Verifies that the specified condition is false.  The assertion fails if it is true.
		/// </summary>
		/// <param name="condition">The expression that should be <c>false</c>.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void IsFalse(bool condition)
		{
			if (condition)
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that the specified condition is false.  The assertion fails if it is true.
		/// </summary>
		/// <param name="condition">The expression that should be <c>false</c>.</param>
		/// <param name="message">The message to display if the condition is <c>true</c>.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void IsFalse(bool condition, string message)
		{
			if (condition)
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that the specified condition is true.  The assertion fails if it is not.
		/// </summary>
		/// <param name="condition">A condition that is expected to be <c>true</c>.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void IsTrue(bool condition)
		{
			if (!condition)
			{
				_Break();
			}
		}

		[Conditional("DEBUG")]
		public static void IsTrue<T>(Predicate<T> predicate, T arg)
		{
			if (!predicate(arg))
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that the specified condition is true.  The assertion fails if it is not.
		/// </summary>
		/// <param name="condition">A condition that is expected to be <c>true</c>.</param>
		/// <param name="message">The message to write in case the condition is <c>false</c>.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void IsTrue(bool condition, string message)
		{
			if (!condition)
			{
				_Break();
			}
		}

		/// <summary>
		/// This line should never be executed.  The assertion always fails.
		/// </summary>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void Fail()
		{
			_Break();
		}

		/// <summary>
		/// This line should never be executed.  The assertion always fails.
		/// </summary>
		/// <param name="message">The message to display if this function is executed.</param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void Fail(string message)
		{
			_Break();
		}

		/// <summary>
		/// Verifies that the specified object is null.  The assertion fails if it is not.
		/// </summary>
		/// <param name="item">The item to verify is null.</param>
		[Conditional("DEBUG")]
		public static void IsNull<T>(T item) where T : class
		{
			if (null != item)
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that the specified value is within the expected range.  The assertion fails if it isn't.
		/// </summary>
		/// <param name="lowerBoundInclusive">The lower bound inclusive value.</param>
		/// <param name="value">The value to verify.</param>
		/// <param name="upperBoundInclusive">The upper bound inclusive value.</param>
		[Conditional("DEBUG")]
		public static void BoundedDoubleInc(double lowerBoundInclusive, double value, double upperBoundInclusive)
		{
			if (value < lowerBoundInclusive || value > upperBoundInclusive)
			{
				_Break();
			}
		}

		/// <summary>
		/// Verifies that the specified value is within the expected range.  The assertion fails if it isn't.
		/// </summary>
		/// <param name="lowerBoundInclusive">The lower bound inclusive value.</param>
		/// <param name="value">The value to verify.</param>
		/// <param name="upperBoundExclusive">The upper bound exclusive value.</param>
		[Conditional("DEBUG")]
		public static void BoundedInteger(int lowerBoundInclusive, int value, int upperBoundExclusive)
		{
			if (value < lowerBoundInclusive || value >= upperBoundExclusive)
			{
				_Break();
			}
		}

		/// <summary>
		/// Verify the current thread's apartment state is what's expected.  The assertion fails if it isn't
		/// </summary>
		/// <param name="expectedState">
		/// The expected apartment state for the current thread.
		/// </param>
		/// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
		[Conditional("DEBUG")]
		public static void IsApartmentState(ApartmentState expectedState)
		{
			if (Thread.CurrentThread.GetApartmentState() != expectedState)
			{
				_Break();
			}
		}

		[Conditional("DEBUG")]
		public static void NullableIsNotNull<T>(T? value) where T : struct
		{
			if (null == value)
			{
				_Break();
			}
		}

		[Conditional("DEBUG")]
		public static void NullableIsNull<T>(T? value) where T : struct
		{
			if (null != value)
			{
				_Break();
			}
		}
	}
}
